The tooth is an interesting structure having layers of soft inner media covered by a hard outer surface. A pulp chamber maintains the blood and nerve supply and is protected by the hard dentin layer, which attenuates shock and pressure experienced during mastication or in the event of a traumatic event. An outer layer of enamel covers the dentin. The inorganic mineral content in dentin is quite low compared to enamel, with the calcium weight fractions in dentin about 28% lower than in enamel. The decreased mineral content in dentin is compensated for by an equivalently elevated weight fraction of organic constituents. Although the Ca:P ratios in both calcium and dentin are about the same, the specific surface areas differ markedly: 77 m2/g for enamel and 94 m2/g for dentin. One reason for the increased surface area of dentin may be attributed to collagen tubules manifested within the dentin matrix, which help provide structure and support.
Tooth enamel is comprised of a heterogeneous arrangement of inorganic mineral and less than 1% organic substances, including proteins and collagen. The overall thickness of human enamel can be up to several millimeters and visually, the apatite crystals bear a hexagonal arrangement, although the actual unit cell pertaining to hydroxyapatite is likely comprised of two different sets of monoclinic crystal arrangements, with one monoclinic arrangement arising from two hexagonal cells. Typical enamel crystallites have dimensions of about 40 nm wide and at least 300 nm long, with adjacent prisms separated interproximally by a substance comprised of organic and inorganic matter that is somewhat more resistant to caries formation. The apatite crystals found in enamel predominantly manifest hydroxyl or carbonate species. Additionally, these crystals may also have magnesium, strontium, and sodium substituted for calcium.
Dissolution of the enamel prisms occurs during an acid attack leading to demineralization. The nature of the acid challenge is distinguished between cariogenic and erosion; for the latter, acid reflux or consumption of acid beverages, for example, leach mineral from the crystal, creating macroscopically smooth and rounded characteristics of the enamel, while the microstructure reveals significant pitting and jaggedness. With respect to the cariogenic type of enamel weakening, acid-producing bacteria, such as Streptococcus mutans, adhere to the tooth and ferment carbohydrates containing sucrose consumed during eating events. This activity produces lactic acid which then eats away at the enamel structure to create subsurface lesions that may ultimately progress to cavitations, or dental caries. Microscopically, the demineralization process occurs primarily at the center surface of the enamel prism and propagates downwards through the body of the prism, ultimately proceeding outwards to the prism walls. The prism surface manifests species such as OH− and CO32− residing at the center of the crystal. Although this occupancy helps to stabilize the apatite structure, these species are highly prone to dissolution relative to Ca2+ and PO43−, which reside on the corners and faces of the crystal arrangement.
The thermodynamic progressions of remineralization to apatite, coupled with the relatively low levels of inorganic mineral constituents naturally found in saliva, are often unable to keep pace with the rate of demineralization. Even further problematic, for instance, salivary flow is often reduced for individuals taking medications, including aspirin or antihistamines. It follows then the already low calcium salivary levels will likely be affected resulting in an increased risk for enamel demineralization.
Other means, such as fluoride, could be utilized to help restore enamel strength more proactively. Fluoride has a rich and clinically-proven history of preventing dental decay. First added to drinking water in low levels, topical fluorides have evolved into such common vehicles as toothpaste and mouth rinses. These relatively inexpensive forms of topical dental therapy are quite appealing and will likely become even more so as the views of patients and practitioners shift even further to prevention instead of restoration, the latter of which is typically considered to be more costly and painful.
Even through fluoride applications and other preventive measures, dental decay still affects the majority of the world's population. A US study conducted by the National Health and Nutrition Examination Survey recently reported that while dental decay has not increased in the last 25 years for most of the US population, dental decay is on the rise in children between 2 and 11 years old. This apparent epidemic suggests that fluoride alone, despite its great clinical success and acceptance, may be insufficient.
Further, while many drinks and other comestibles are currently fortified with calcium, the calcium is typically added in the form of a highly soluble precursor, such as calcium gluconate, calcium lactate or the like. While such highly soluble calcium is advantageous for quick and efficient absorption through the stomach and intestines, such rapid dissolution is less desirable for a calcium supplement intended to reside in the mouth for sufficient time to promote remineralization of the teeth. For such remineralization a relatively slow and steady calcium supply is more desirable. Tricalcium phosphate is a cheap, plentiful and rich calcium source with a very slow calcium release rate. Unfortunately, conventional calcium phosphate materials dissolve too slowly and such technologies are only marginally effective in providing useful quantities of minerals to the teeth.
Thus, there remains a need for mineral delivery compounds that reside in the mouth and that directly boost remineralization efficacy via direct application to the tooth. The present novel technology addresses this need.